Radio ranging system



April 17, 1956 v. M. HAYWOOD ETAL 2,742,633

RADIO RANGING SYSTEM 2 Sheets-Sheet 1 Original Filed Jan. 5, 1952INVENTOR VERNON n HAYWOOD ROBERT L. CAYOUET'TE HOWARD c. BY ,9? MawTURNAGE ATTORNEYS United States RADIO RANGING SYSTEM Vernon M. Haywood,Robert L. Cayouette, and Howard (1. Turnage, Hampton, Va.

Original application January 5, 1952, Serial No. 265,116. and thisapplication June 25, 1954, Serial No. i

4 Claims. (Cl. 343-12) This invention relates to radio ranging systems.More particularly, the invention relates to such systems which are basedupon phase comparison of beat frequencies developed from carrierfrequencies separated by a relatively low frequency such as an audiotone.

This application is a division of our copending application Serial No.265,116, filed January 5, 1952, now Patent 2,709,253.

In the past, radio ranging systems of the above mentioned type have beenvery successfully employed in which a pair of transmitters is used, bothtransmitters of the pair being tuned to operate in the same channel butseparated in frequency by an audio tone, with one transmitter at a firstor fixed station and the other at a second or mobile station. Thosesystems further employ a pair of receivers, one located at the firststation and the other at the second station, the receivers each beingtuned to receive transmissions from both of the transmitters to detectthe audio tone as a beat frequency. A return link is then customarilyprovided from one station to the other to relay the beat frequencies toa common point which is usually, but not necessarily, at one or theother of the stations. So arranged, the known systems provide anextremely accurate method of ranging. As an example, one system whichhas been widely used is fully described and claimed in United StatesPatent 2,528,141, patented October 31, 1950, to Charles E. Hastings.Referring particularly to the elliptical ranging systems described inthat patent, it is clear that when the spacing between the transmitterand receiver at each station is small concerned with the distancebetween stations, the elliptical paths of constant beat frequency phasesubstantially become circles and the system remains sensitive to range,but becomes insensitive to direction.

However, in systems as described in the above mencomes the limitingfactor in the range of operation. In

other words, with the transmitter arranged to transmit sufiicient powerso that the signal may be picked up at the other station, the adjacentreceiver is swamped by the transmitter.

The primary object of the present invention is to overcome the abovedifiiculties. Briefly stated, the present system is as above describedin the use of a separate frequency for each transmitter-receivercombination. Preferably, one frequency will differ by a relatively lowfrequency from being a harmonic of the other frequency. Fiu'therdistinction over the above system also lies in providing for laneidentification by use of a differential device connected withintegrating phasemeters tied in with systems operating on slightlydifferent frequencies.

The problem of separating the transmitting and receiving antennas hasbeen done away with so completely in systems according to the presentinvention that a trans- 2,742,638 Patented Apr. 17, 1956 distancesbetween stations over very great ranges and yet permit an absoluteminimum of separation of transmitter and receiver units at either orboth stations. I

It is a further object of this invention to provide a system asmentioned in the mitters will be employed to separate the transmissionchannels and yet provide excellent means for comparing beat frequencyphase angles to indicate range.

It is a further object of this invention to provide a radio rangingsystem in which a ranging frequency is employed as a return link.

It is a further object of this invention to provide lane identificationin radio ranging and navigation systems by use of slightly differentfrequencies and in which integrating phasemeters connected with adifferential indicating device may be employed.

.Further objects and the entire scope of the invention will become morefully apparent from the following detailed description and from theappended claims.

The invention may be best understood with reference to the accompanyingdrawings, in which: i Figure 1 shows an example of a basic systemaccording to the present invention. I

Figire 2 shows a system according to the invention in which one of theranging frequencies is employed as a return link for relaying a detectedbeat frequency back'to one of the stations, and

Figure 3 shows a system according to the present invention for providinga means of positive lane identification.

first station and 12 generally designates a second station.-.

Either of these stations may be fixed or movable as desired. All that isinvolved in the system is the measurement of absolute range between thetwo stations. A transmitter 14 on frequency f is located at station 12.Transmitter 14 will have sufficient power to provide a signal atreceiver 16 at station 10 of frequency f and will also produce a smallamount of second harmonic 2; which wil be picked up by a receiver 18 atstation 12.

At station 10 there is a transmitter 20 operating on 2) plus an audiotone f Transmitter 20 may be of the well known type which uses a crystaloscillator operating on one-half of the output frequency, which in thiscase will be and a small amount of this frequency will unavoidably beradiated. As an example of operating values f may be 400 C. P. S. and 7may be between 2 and 6 magacycles.

Receiver 16 tuned to frequency f will detect a heat frequency Ipreceding paragraph in which. available harmonic and sub-harmonicradiations of trans-.

The frequency f passing filter 40 may be applied over line 44 to oneside of an integrating phasemeter 46 and the frequency passing filter 42may be applied over line 48 to a frequency doubling circuit 50.Accordingly, frequency 1 will appear at the output of doubler circuit 50and may be applied over line 52 to the other side of phasemeter 46. Itwill be clear from the foregoing that the same operation is realized atphasemeter 46 as is .the case with the system of Figure 1, but with theadvantage that the relay return link at frequency f1 is eliminated.

In the systems of Figures 1 and 2, tracking cannot be started at anunknown point because lane ambiguities will be present. However, oncestarted a record of position may be maintained by use of integratingphasemeters and/or pen recorders.

Referring now to Figure 3, lane identification can be directly obtainedwithout ambiguity at any random point by using two complete systemsoperating on slightly different basic frequencies. To best explain thissystem the description will proceed with specific examples of usablefrequencies. However, no limitation to these frequencies is intended.

In Figure 3 at station 12 the transmitter 60 may operate at 2.5 me. anda transmitter 62 may operate at 2.45 me. Also, at station 12 is areceiver 64 tuned to me. and a receiver 66 tuned to 4.9 me.

At station a transmitter 68 operates at 5 mc.+500 c. and transmitter 70operates at 4.9 mc.+400 c. Also, at station 10 receiver 72 is tuned to2.5 me. and receiver 74 is tuned to 2.49 me.

The result of the foregoing, as indicated by the transmission lanes inFigure 3, is that, at station 10 the output of receiver 72 on line 76 isa heterodyne signal at 250 c. and the output from receiver 74 on line 78is a 200 c. heterodyne signal. These heterodyne signals on lanes 76 and78 are applied to a modulating circuit 80 which modulates a return linktransmitter 82 which operates on any convenient return link frequencyf1.

At station 12 the output of receiver 64 on line 84 is a 500 c.heterodyne signal and the output of receiver 66 on line 86 is a 400 c.heterodyne signal. Line 84 carrying the 500 c. signal is applied to oneside of a phasemeter 88 and line 86 carrying the 400 c. signal isapplied to one side of an indicating phasemeter 90.

The return link frequency fl is received at receiver 92 and thefrequencies derived from receiver 92 appearing on line 94 are doubled indoubler circuit 96 and then applied over lines 98 and 100 to bandpassfilters 102 and 104, respectively. Filter 102 may be arranged to passonly 500 cycle signals and filter 104 pass only 400 cycle signals. Theoutput of filter 102 is applied over line 106 to the second input ofphasemeter 88 and the output of filter 104 is applied over line 198 tothe second input of phasemeter 90.

The phasemeters 88 and 90 may be interconnected with a simpledifferential gear device 110 which may be provided with a pointer 112for indicating the lane in which the opposite station (in this casestation 10) is 10- cated.

In operation, it may be considered that when the phasemeter 88 operatingin the 5 me. system makes 50 revolutions, for example, the phasemeter 90operating in the 4.9 mc. system makes 49 revolutions, etc. Accordingly,the difference between the two phasemeter readings may be used as adirect indication of the lane from zero to fifty in which station 10 islocated. In other words, if the system is turned on with station 12in anunknown lane, the phasemeters will indicate a differential which willnot be the same for any other lane. The number of lanes which can beaccommodated will depend on the operating frequencies.

' In any of the foregoing systems it will be understood that with theuse of conventional phasemeters alone a continuous track of phase changemay be made by use of a pen recorder.

It is of considerable interest and importance to note that in the abovesystems any drift of the transmitter at station 10 is of no importance.In other words, the basic frequencies of the two transmitters need notbe true harmonics and need not be directly synchronized as is requiredin some types of radio ranging systems.

It is further of interest that the transmitters employed may be ofentirely conventional construction. The second harmonic and thesub-harmonic radiated by the transmitter as above described are purelyincidental. Neither is radiated with enough power in ordinary usage toviolate any broadcasting regulations.

it is further to be noted that the desired harmonics produced by thetransmitters need not be transmitted through space. That is, as abovementioned, the receiver and transmitter may-be coupled to a commonantenna.

Although in the foregoing descriptions two frequencies having anapproximate ratio of 2 to 1 have been described, other ratios can beused equally well, such as 3 to 1, and 4 to 1. Also, more complex ratiossuch as 2 to 3, 3 to 4 and 3 to 5 can be used. However, these systemswould require special transmitters and would be undesirable for thatreason.

It will be understood that the above detailed description has been madeonly for purposes of illustration and is not intended to limit the scopeof the invention. On the contrary, the scope of the invention is to bedetermined from the appended claims.

We claim:

1. A radio ranging system comprising a first station and a secondstation, a first transmitting means and a first receiving means locatedat the first station, a second transmitting means and a second receivingmeans located at the second station, the first transmitting means beingadapted for operation at a first frequency and arranged to produce atleast a limited amount of signal at a second frequency related to thefirst frequency, the second transmitting means being adapted to operatesubstantially at the said second frequency but difiering therefrom by arelatively low frequency and arranged to produce at least a limitedamount of signal at a third frequency related to the second frequencytogether with the low frequency, the first receiver being adapted toheterodyne the signal of second frequency from the first transmittingmeans and the transmission from the second transmitter to produce afirst beat signal at the said low frequency, the second receiver beingadapted to heterodyne the transmission from the first transmitter andthe signal of said third frequency received from the second transmitterto produce a second beat signal, frequency altering means for causingthe said first and second heat signals to correspond in frequency, meansfor relaying the beat signals to a common location, and means at thecommon location for comparing the phase angles of the beat signals todetermine the spacing between the first and second stations, the systemfurther including a third transmitting means and a third receiving meansat the first station and a fourth transmitting means and a fourthreceiving means at the second station, the third and fourth transmittingand receiving means being adapted for operation as a unit with the unitcomprising the first and second transmitting and receiving means but ata different set of frequencies, and means for comparing the beatfrequency phase angles of each of the systems as detected at the commonlocation for directly determining the spacing between the first andsecond stations in terms of the number of radio frequency wave lengthsbetween the first and second stations.

2. A system as in claim 1 in which the means for comparing the saidphase angles of the two units comprises a differential device connectedbetween the phase angle determining means of each unit.' i f '3; A radioranging system comprising ajfirst station and a second station, firstand third transmitting means and first and third receiving means locatedat'jthe 'first station, second and fourth transmittingmeans and secondand fourth receiving meanslocat'ed atthe second station, the first andsecond transmitting means being tuned to opcrate, at firsttfrequenciesdiffering by a first relatively'low frequency, the third andlfourthtransmitting means being tuned to operate at second frequenciesdiffering by a sec- 0nd relatively low frequency, the first and secondreceivers being tuned to detect a beat signal of said first lowfrequency, means for determining the phase angle'between the'beat signalof said first low frequency, the third and fourth receivers being tunedto 'detect'beat signals of said second low frequency, means fordetermining the phase angle'between the beat signals of said second lowfrequency, and differential means connected with'the first andsecondphase determining means for indicating direct ly withouttambiguitythe distance of the second station from the'first station.

a 1:8 H 4. A radio ranging :system comprising a first station and a. andfirst 'arid'fliir'd receiving means located .at thetfirst station,second and fourth transmitting means and second and fourthtreceivingmeansilocated at the second station, the first and second transmittingmeans being tuned to operate at first frequencies differing by a firstrelatively lo'w' freqiren'cy, 'thefihird and fourthtransmittingmeans'f'be'ing'tunedao operate at second 'frequenciesdifferin g by a second re'latively'low 'freqeuncy, the first and second-receivers beingfltuned to detect a beat signal of said first lowfrequent y; means for determining thephase angie between the beatsi'gnal-of said first low frequency, the third and fourthmeceivers'beingtun'ed to detect beat signals of saidfieconjd iow frequency, meansfor determining the phase angle betweenthe beat signals of said secondlow frequency-for indicating directly without ambiguity the -distancedfthe second station from the first station.

.:N.o referenceszcited.

on?! station, first and third transmitting 'means T

